The mechanical pump comprises a pump rotor with radially slidable vanes rotating in a shiftable control ring, whereby the control ring envelopes numerous pump chambers. The shifting of the control ring is not necessarily a linear movement, but can also be a pivoting movement. The pump chambers rotate through a charge and a discharge zone inside the control ring. The pump further comprises a pretensioning element which pushes the control ring to a high pumping volume direction. A first control chamber pushes the control ring to a low pumping volume direction, and a second control chamber pushes the control ring to a high pumping volume direction if the lubricant is pressurized. The pump also comprises a pump outlet which is connected to the first control chamber. Both control chambers, i.e., the first and the second control chamber, are connected to each other via a throttle valve. Both control chambers can have a different circumferential extend around the control ring, so that the effective surfaces of the two control chambers and the respective moment arms are different. Both control chambers act against each other, i.e., act in different pumping volume directions.
WO 2006 066405 A1 describes a pump where the displacement of the lubricant is controlled by the eccentricity of the control ring. The eccentricity of the control ring is controlled by the equilibrium forces between the first control chamber, the second control chamber and the pretensioning element. When the pump rotor rotates in the control ring, the pump rotor causes a compression of the lubricant in the discharge zone. The lubricant is compressed at maximum in the discharge pump chamber which is located at the end of the discharge zone, i.e., the pump chamber with the minimum volume in the discharge zone. This maximum compression of the lubricant can cause high local pressure peaks, especially at high rotating speeds and if the control ring is positioned at a high pumping volume position, so that the equilibrium forces between the first control chamber, the second control chamber and the pretensioning element are temporarily disturbed. As a consequence, the lubricant flow rate can be temporarily incorrect and not adapted to the engine demand.